Have just installed a new hot water system, and still no pressure.. any ideas please...

Could use more detail.

Is this in all faucets?

Remove aerator and clean. Let water run for a few sec to clear lines. Does this help?

Be sure that the shut off valve is open.

Chuck

have just installed a new hot water system, and still no pressure.
By "new hot water system" do you mean just a water heater or did you replace the pipes also?
Do you have a pressure loss in all taps? More details please. Tom